1. Field of the Invention
The present invention concerns a unitary exhaust gas housing for a turbo-engine fitted with a temperature control device.
2. Summary of the Prior Art
It is usual practice with gas turbine engines to provide downstream of the turbine a one-piece housing comprising radial struts linking outer and inner annular parts which together form a duct for the flow of the hot gases.
One of the applications particularly envisaged by the invention is the case of an aircraft propulsion unit comprising a gas generator downstream of which are associated free turbines, in which the continuity of the aerodynamic flow path for the hot gases is ensured by an assembly of the above-mentioned type which, in this instance, is called the inter-turbine structure. This unitary assembly, consisting for example of a single cast component, forms, in this instance, four coaxial rings connected by a series of shaped struts; an outer ring which forms the outer skin of the engine of this region, two intermediate rings which form the outer and inner walls of the gas path, and an inner box-section ring forming the hub and central support of the whole structure. In the course of operation of the engine, large temperature gradients appear within this interturbine structure between components in direct contact with the flow of hot gases emerging from the gas generator turbines, and the internal hub which remains relatively cool. These thermal gradients are the cause of high mechanical stresses, particularly in the form of thermal shocks during the transient operating phases of the engine, such as, in the case of aircraft use, during take-off, and are prejudicial to good component performance in service. Attempts to solve the problem, for example, by heating the hub by means of air drawn from that circulated within the struts of the structure have proved inadequate.
The invention aims to solve the problem whilst, at the same time, avoiding measures which would prejudice the efficiency of the thermodynamic cycle during stable operating phases of the engines, notably when cruising in the case of aircraft, and to this end, proposes to limit the periods during which gas is withdrawn for heating the hub to the transient phases of operation, during which heating of the inner hub of the unitary structure is useful.